Reflection type display apparatus

ABSTRACT

A reflection type display apparatus wherein an electroplating is used to modulate light, at least one of a reflectance and an absorptance of a first surface, which contacts the first electrode, of an electroplating film  10  formed on the first electrode  2  and that of a second surface, which does not contact the second electrode, of the electroplating film  10  formed on the second electrode  4  are different. When the electroplating film  10  is formed on the first electrode  2,  reflection light from the first surface is used for displaying. When the electroplating film  10  is formed on the second electrode  4,  reflection light from the second surface is used for displaying.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflection type display apparatusand, more particularly, to a reflection type display apparatus which hasan electrode that is come into contact with an electrolyte solution andin which an electroplating film is formed on the electrode and anelectroplating is used for modulating light.

2. Description of the Related Art

As a display apparatus in which visibility is high and electric powerconsumption is small, electronic paper is vigorously being developed. Anexample in which a color filter is combined with a display apparatususing an electroplating has been disclosed in the Official Gazette ofJapanese Patent Application Laid-Open No. H11-101994. According to theOfficial Gazette of Japanese Patent Application Laid-Open No.H11-101994, the display apparatus has a structure in which a silver saltsolution is arranged between a working electrode and a counterelectrode, a color filter is arranged on a light incident side of theworking electrode (the side opposite to the side of the workingelectrode where the silver salt solution is arranged), and a whitebackground plate is arranged on the counter electrode (on the side ofthe counter electrode where the silver salt solution is arranged). Inthe case of allowing silver to be deposited in the working electrode,the light which has entered through the color filter is absorbed bydeposited silver. On the contrary, if silver is not deposited in theworking electrode, the light which has entered through the color filterpasses through the working electrode, is reflected by the whitebackground plate, and passes through the working electrode and the colorfilter, thereby performing a color display.

SUMMARY OF THE INVENTION

According to the Official Gazette of Japanese Patent ApplicationLaid-Open No. H11-101994, the display apparatus has a structure in whichthe incident light passes through the color filter before it isreflected by a reflection layer. Pixels corresponding to three primarycolors are necessary to display a white color by such a structure. Eachpixel reflects only a monochromatic color and, in the incident light,color components which are not reflected are absorbed by a color filterof each pixel. For example, in the pixel which reflects a red color,blue and green components are absorbed. In the pixel which reflects ablue color, red and green components are absorbed. In the pixel whichreflects a green color, blue and red components are absorbed. Therefore,at the time of the white display, the red component is absorbed in theblue and green pixels, the blue component is absorbed in the red andgreen pixels, and the green component is absorbed in the red and bluepixels. In other words, an area adapted to reflect the red color isequal to ⅓ of the whole area of the display apparatus. This is true ofgreen and blue. Since the light of each color is reflected only by thearea of ⅓ as mentioned above, the whole reflectance at the time of thewhite display is equal to only ⅓ even when considering only an effectivereflection area ratio of each color. It is, therefore, demanded toimprove the reflectance.

It is an object of the invention to provide a reflection type displayapparatus which can perform a dichroic display by using anelectroplating film and, more particularly, to provide a reflection typedisplay apparatus in which a reflectance at the time of a white displayis high and a good black display can be performed.

Another object of the invention is to provide a reflection type displayapparatus which can perform a white display at a high reflectance andcan be applied to a better color display.

According to the invention, there is provided a reflection type displayapparatus using an electroplating for modulating light, comprising: afirst electrode; a second electrode; and an electrolyte solutionarranged between the first and second electrodes, wherein theelectroplating is formed from the electrolyte solution onto one of thefirst and second electrodes by setting a direction of current flowingbetween the first and second electrodes, a first surface of theelectroplating formed on the first electrode such that theelectroplating contacts the first electrode through the first surface isdifferent in at least one of a light reflectance and a light absorptancefrom a second surface of the electroplating formed on the secondelectrode such that the electroplating does not contact the secondelectrode through the second surface, and a displaying is performed by areflection light from the first surface in case that the electroplatingis formed on the first electrode, while a displaying is performed by areflection light from the second surface in case that the electroplatingis formed on the second electrode.

According to the invention, the reflection type display apparatus whichcan perform the dichroic display by using the electroplating film and,more particularly, in which the reflectance at the time of the whitedisplay is high and the good black display can be performed can beobtained.

According to the invention, the reflection type display apparatus whichcan perform the white display at the high reflectance and can performthe color display can be obtained.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view illustrating a schematic constructionof the first embodiment of a reflection type display apparatus of theinvention.

FIG. 2 is a schematic cross sectional view illustrating anotherdisplaying method of the reflection type display apparatus of the firstembodiment.

FIG. 3 is a cross sectional view illustrating a schematic constructionof the second embodiment of a reflection type display apparatus of theinvention.

FIG. 4A is a cross sectional view illustrating a schematic constructionof the third embodiment of a reflection type display apparatus of theinvention.

FIG. 4B is a cross sectional view for describing an operation principleof a full-color display in the third embodiment of the reflection typedisplay apparatus of the invention.

FIG. 4C is a constructional diagram illustrating a conceptualconstruction of the full-color display in FIG. 4B.

FIG. 5 is a schematic cross sectional view illustrating reflection,transmission, and absorption of light which entered a pixel.

FIG. 6 is a cross sectional view of a pixel of a reflection type displayapparatus of the fourth embodiment of the invention.

FIG. 7 is a cross sectional view of a pixel of a reflection type displayapparatus of the fifth embodiment of the invention.

FIG. 8 is a cross sectional view of a pixel of a reflection type displayapparatus of the sixth embodiment of the invention.

FIG. 9 is a perspective view illustrating the reflection type displayapparatus in the case of performing a passive matrix driving.

FIGS. 1A, 10B and 10C are plan views illustrating constructionalexamples of electrodes 4 and 5 of the invention.

FIG. 11 is a circuit constructional diagram of the reflection typedisplay apparatus according to the invention in the case of performingan active matrix driving.

FIG. 12 is a circuit diagram illustrating a control circuit forcontrolling the flowing direction of a current.

FIGS. 13A and 13B are circuit diagrams each illustrating a controlcircuit for controlling the flowing direction of the current.

FIG. 14 is a cross sectional view of a display apparatus of the seventhembodiment of the invention.

FIGS. 15A and 15B are schematic diagrams each illustrating a layer inwhich conductive fine particles are dispersed in an insulator having airgaps therein according to the invention.

FIG. 16 is a schematic diagram of an electrode of the first comparativeexample.

FIGS. 17A and 17B are schematic diagrams each illustrating an electrodeof the second comparative example.

FIGS. 18A and 18B are diagrams illustrating display memory performanceof the display apparatus of an embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the invention will be described in detailhereinbelow with reference to the drawings.

First Embodiment

FIG. 1 is a cross sectional view illustrating a schematic constructionof the first embodiment of a reflection type display apparatus of theinvention. A pixel 40 in FIG. 1 illustrates a pixel in the case where anelectroplating film 10 is formed on a first electrode 2. A pixel 41 inFIG. 1 illustrates a pixel in the case where the electroplating film 10is formed on a second electrode 4.

In FIG. 1, the first electrode 2 having a light transmitting property isformed on a substrate 1 having a light transmitting property (serving asa first substrate) and the second electrode 4 having a lighttransmitting property is formed on a substrate 6 having a lighttransmitting property (serving as a second substrate). The firstelectrode 2 and the second electrode 4 are arranged so as to face eachother through an electrolyte solution 3. Although the second electrode 4may have the light transmitting property, it may be made of a metalwhich does not have the light transmitting property. The substrate 6provided with the second electrode 4 may not have the light transmittingproperty. The electrolyte solution 3 contains two or more kinds of metalelements serving as metal ions. It is sufficient that the lighttransmitting electrode substantially has the light transmittingproperty. It is not always necessary to form the electrode having thelight transmitting property by a transparent electrode such as an ITO orthe like but it can be formed by a thin metal film or a mesh structureor comb-tooth structure of a metal (this is true of embodiments, whichwill be described hereinafter), can be also used.

When the first electrode 2 is assumed to be a cathode, the secondelectrode 4 is assumed to be an anode, and a current is supplied tothose electrodes, the metal ions contained in the electrolyte solution 3are reduction-deposited on the surface of the first electrode 2. Asillustrated in the pixel 40, the metal is electroplated onto the firstelectrode 2, so that the electroplating film 10 is formed. In thisinstance, the color of the deposited electroplating film is influencedby compositions of the electrolyte solution 3. For example, when theelectrolyte solution 3 contains silver and copper, an interface (thefirst surface of the electroplating film) between the first electrode 2and the electroplating film 10 becomes a non-colored mirror surface andreflects the incident light. Therefore, when seen from the firstelectrode 2 side, the white color as a first color is observed.

On the other hand, when the second electrode 4 is assumed to be thecathode, the first electrode 2 is assumed to be the anode, and a currentis supplied to those electrodes, the metal ions contained in theelectrolyte solution 3 are reduction-deposited on the surface of thesecond electrode 4. As illustrated in the pixel 41, the metal iselectroplated onto the second electrode 4, so that the electroplatingfilm 10 is formed. When the electroplating film 10 is seen from thefirst electrode 2 side, the surface of the electroplating film 10 whichis not come into contact with the second electrode 4 (the second surfaceof the electroplating film) is observed. In this instance, the color ofthe deposited electroplating film is influenced by the compositions ofthe electrolyte solution 3. For example, when the electrolyte solution 3contains silver and copper, the surface of the electroplating film has arough concave/convex shape and absorbs the incident light. Therefore,the black color as a second color is observed.

In order to form the electroplating film in which the colors of theobverse and reverse surfaces differ, like an electrolyte solution 3containing silver and copper as shown as an example in the embodiment,the electrolyte solution contains the two or more kinds of metalelements serving as metal ions. As two or more kinds of metal elements,the electrolyte solution contains at least: a first metal elementserving as an electroplating seed; and a second metal element whoseoxidation-reduction potential is close to that of the first metalelement. In the embodiment, silver is used as a first metal element andcopper is used as a second metal element.

A reason why the oxidation-reduction potential of the second metalelement is close to that of the first metal element will be describedhereinbelow. It is assumed that as main components, the electrolytesolution contains: a first substance whose oxidation-reduction potentialis higher than that of the first metal element; and a second substancewhich is a main component in the solution and whose oxidation-reductionpotential is lower than that of the first metal element. For example,when a dimethylformamide solution is used as an electrolyte solution,the first substance corresponds to bromine and the second substancecorresponds to hydrogen. Assuming that the oxidation-reductionpotentials of the first substance and the second substance are set tothe first electric potential and the second electric potential,respectively, the oxidation-reduction potential of the second metalelement in the electrolyte solution is lower than the first electricpotential and is higher than the second electric potential. According tothe foregoing example, when the oxidation-reduction potential of silverserving as a first metal element is assumed to be a reference (0V), theoxidation-reduction potential (the first electric potential) of bromine(the first substance) is higher (+0.2V) than the oxidation-reductionpotential of silver and the oxidation-reduction potential (the secondelectric potential) of hydrogen (the second substance) is lower (−0.8V)than the oxidation-reduction potential of silver. Theoxidation-reduction potential of copper serving as a second metalelement is located between the first electric potential and the secondelectric potential (−0.3V). The second metal element in such a state isdefined as a second metal element in which “oxidation-reductionpotential is close to that of the first metal element”.

Ordinarily, in the electroplating which is used for light modulation,the electrolyte solution is designed so that oxidation/reduction of theunexpected substances does not occur in a range where the electricpotential of the electrode changes. That is, the substance whoseoxidation-reduction potential is close is not contained in theelectrolyte solution so that the substances other than the metal to beelectroplated are not reduced on the electrode. This is because if aplurality of metals are oxidized/reduced on the same electrode, aturbulence occurs and the clean electroplating film is not deposited.However, in the embodiment, the two kinds of metal elements having theoxidation-reduction potentials within the range where the electricpotential of the electrode changes are purposely contained in theelectrolyte solution, thereby intentionally causing the turbulence. Dueto the turbulence, the deposited electroplating film grows into thelarge concave/convex shape, so that the colors of the obverse andreverse surfaces of the electroplating film differ largely.

In the pixel 40, in a state where the electroplating film has beenformed on the first electrode 2, when the second electrode 4 is assumedto be the cathode, the first electrode 2 is assumed to be the anode, anda current is supplied to those electrodes, the electroplating film isformed onto the second electrode 4 and the electroplating film formed onthe first electrode 2 is dissolved. Therefore, by switching the currentflowing direction in the first electrode 2 and the current flowingdirection in the second electrode 4, the electroplating film can beformed onto an arbitrary one of the first electrode 2 and the secondelectrode 4 in the same pixel.

By constructing the reflection type display apparatus by using such aprinciple, the monochromatic (black and white) dichroic display can beswitched. By controlling a thickness of electroplating film, a gradationdisplay can be also performed.

In the reflection type display apparatus of the embodiment, by allowingthe second electrode 4 to have the light transmitting property and byallowing the substrate 6 to have the light transmitting property, thedichroic display in which the colors of the obverse and reverse surfacesdiffer can be also performed as illustrated in FIG. 2. That is, when theelectroplating film 10 is formed onto the first electrode 2, asillustrated in FIG. 2, for example, in the case where the electrolytesolution 3 contains silver and copper, when the electroplating film 10is seen from the first electrode 2 side, the white color as a firstcolor is observed. When it is seen from the second electrode 4 side, theblack color as a second color is observed. In this manner, the dichroicdisplay in which the colors of the obverse and reverse surfaces differcan be also performed. When the electroplating film 10 is formed ontothe second electrode 4, in the case where the electroplating film 10 isseen from the first electrode 2 side, the black color as a second coloris observed. When it is seen from the second electrode 4 side, the whitecolor as a first color is observed. In this manner, the dichroic displayin which the colors of the obverse and reverse surfaces differ can beperformed. The substrates 1 and 6 are omitted for simplicity ofdescription in FIG. 2.

Either the first electrode 2 or the second electrode 4 may be formed bya metal wire such as a platinum wire. In this case, since the platinumwire is hardly observed, the reflection type display apparatus asillustrated in FIG. 2 can be formed.

The dichroic display in which the colors of the obverse and reversesurfaces differ and which is performed by using the electroplating filmformed on the first electrode 2 and the dichroic display in which thecolors of the obverse and reverse surfaces differ and which is performedby using the electroplating film formed on the second electrode 4 asdescribed above can be combined. By using such a combination, areflection type display apparatus in which the dichroic display can beperformed with respect to each of the obverse and reverse surfaces canbe also realized.

Second Embodiment

FIG. 3 is a cross sectional view illustrating a schematic constructionof the second embodiment of a reflection type display apparatus of theinvention. In FIG. 3, three pixels 101, 102, and 103 are illustrated.The reflection type display apparatus is constructed by laminating: thefirst substrate 1 which protects the surface; the first electrode 2; thecolored second electrode 4 which faces the first electrode 2 through theelectrolyte solution 3; a third electrode 5 which is come into contactwith the same electrolyte solution as that of the first electrode 2 andthe second electrode 4; and the second substrate 6. The first electrode2 and the first substrate 1 have the light transmitting property. Theelectrolyte solution 3 contains two or more kinds of metal ions. An areaof the third electrode 5 is smaller than an area of the second electrode4. The second substrate 6 may or may not have the light transmittingproperty. FIG. 3 illustrates the case where in the pixel 101, theelectroplating film 10 is formed on the second electrode 4, in the pixel102, the electroplating film 10 is formed on the first electrode 2, andin the pixel 103, the electroplating film is formed on the thirdelectrode 5, respectively.

When the first electrode 2 is assumed to be the cathode, the secondelectrode 4 and the third electrode 5 are assumed to be the anodes, anda current is supplied to those electrodes, the metal ions contained inthe electrolyte solution 3 are reduction-deposited on the surface of thefirst electrode 2 as illustrated in the pixel 102, so that the metal iselectroplated. In this instance, the color of the deposited metal filmis influenced by the compositions of the electrolyte solution 3. Forexample, when the electroplating liquid contains silver and copper, theinterface (the first surface of the electroplating film) between thefirst electrode 2 and the electroplating film becomes a non-coloredmirror surface and reflects the incident light. Therefore, when seenfrom the first substrate 1 side, the white color as a first color isobserved.

On the other hand, when the second electrode 4 is assumed to be thecathode, the first electrode 2 and the third electrode 5 are assumed tobe the anodes, and a current is supplied to those electrodes, theelectroplating film is electroplated onto the surface of the secondelectrode 4 as illustrated in the pixel 101. At this time, when seenfrom the substrate 1 side, the obverse surface of the electroplatingfilm which is not come into contact with the electrode (the secondsurface of the electroplating film) is observed from the surface.However, the surface has a rough concave/convex shape and absorbs theincident light. Therefore, the black color as a second color isobserved.

When the third electrode 5 is assumed to be the cathode, the firstelectrode 2 and the second electrode 4 are assumed to be the anodes, anda current is supplied to those electrodes, the metal ions contained inthe electrolyte solution 3 are reduction-deposited on the surface of thethird electrode 5 as illustrated in the pixel 103, and the metal iselectroplated. At this time, since all of the metals deposited on thesurfaces of the first electrode 2 and the second electrode 4 are alsodissolved, the color of the second electrode 4 is observed from theobverse surface through the first electrode 2 having the lighttransmitting property.

The second electrode 4 may use the color of the material itself or mayuse a selective reflection due to the laminated structure. For example,when the second electrode 4 is formed by a laminated structure of TiNand AlCu, the reflection color can be adjusted by an interferencedepending on a film thickness of TiN.

Even if the second electrode 4 is formed by a material having a lighttransmitting property and a colored substance is arranged on thesupporting substrate 6, a similar effect is obtained.

If the reflection type display apparatus is formed by using such aprinciple, a trichromatic display can be switched.

With respect to the electroplating film which is formed/extinguished onthe surface of the first electrode 2 and the electroplating film whichis formed/extinguished on the surface of the second electrode 4, thetransmitting ratio or reflectance of the light can be adjusted byadjusting a thickness of electroplating film.

Third Embodiment

FIG. 4A is a cross sectional view illustrating a schematic constructionof the third embodiment of a reflection type display apparatus of theinvention. The embodiment relates to the apparatus for performing afull-color display by arranging a plurality of pixels in a matrix form.A construction of the third embodiment differs from the construction ofthe second embodiment with respect to a point that the second electrode4 and the substrate 6 have the light transmitting property andreflection plates 17, 18, and 19 in which wavelength ranges of the lightwhich is reflected are red, blue, and green are arranged below thesecond electrode 4 and the third electrode 5, respectively. In thepixels 101 and 102, a display similar to that in FIG. 3 is performed.However, in the pixel 103, the second electrode 4 and the substrate 6transmit the light and the light is reflected by the reflection plate19, so that the color of the reflection plate 19 can be seen.

Although the reflection plate is used as a reflector in the embodiment,the reflector can be formed by forming a reflecting layer adapted toreflect the light of a specific color onto the substrate 6 pixel bypixel by printing or the like. The reflector may be formed by forming acolor filter onto the substrate 6 and arranging a reflection plate ontothe color filter. Although FIG. 4A illustrates an example in which theelectrodes 4 and 5 are formed on one surface of the substrate 6 and thereflection plate as a reflector is formed onto the opposite surface,even if the reflector such as a reflection plate or the like is comeinto contact with the electrolyte solution, there is no problem. Thereflector may be provided between the substrate 6 and the electrodes 4and 5 so long as the electrodes 4 and 5 can be formed on the reflector.

A principle of performing the full-color display will now be describedhereinbelow with reference to FIGS. 4B and 4C. FIG. 4B is a crosssectional view for describing an operation principle of the full-colordisplay in the third embodiment of the reflection type display apparatusof the invention. FIG. 4C is a constructional diagram illustrating aconceptual construction of the full-color display in FIG. 4B. In FIG.4B, the electroplating films which are formed on the surfaces of thesecond electrodes 4 of the pixels 101, 102, and 103 are constructed asblack films and are illustrated as first light modulating layers 11, 13,and 15 for adjusting light absorptances in a range from 0 to 100%. Whenthe light absorptance is equal to 0, this means a state where noelectroplating film is formed or the thickness of electroplating film isso thin that the light absorption is not perceived. The electroplatingfilms which are formed on the surfaces of the first electrodes 2 of thepixels 101, 102, and 103 are constructed as white films and areillustrated as second light modulating layers 12, 14, and 16 foradjusting light reflectances in a range from 0 to 100%. When the lightreflectance is equal to 0, this means a state where no electroplatingfilm is formed or the thickness of electroplating film is so thin thatthe light reflection is not perceived.

In the reflection type display apparatus of the embodiment, it is notalways necessary that the absorptance and the reflectance can becontrolled in the whole range from 0 to 100%, but can be also controlledin a range from about 30 to 70%. Although the expression such as 0%,100%, or the like is conceptually used hereinbelow, those values are notessential requirements of the embodiment.

Now, assuming that a transmitting ratio, a reflectance, and anabsorptance of each of the first light modulating layers 11, 13, and 15are equal to T₁, R₁, and A₁, respectively, and a transmitting ratio, areflectance, and an absorptance of each of the second light modulatinglayers 12, 14, and 16 are equal to T₂, R₂, and A₂, respectively, thefollowing equations (1) and (2) are satisfied.

T ₁=1−A ₁ −R ₁   (1)

T ₂=1−A ₂ −R ₂   (2)

Since the first light modulating layer is constructed by the blackelectroplating films, it may be considered that the reflectance R₁ isequal to 0. Since the second light modulating layer is constructed bythe white electroplating films, it may be considered that theabsorptance A₂ is equal to 0. Therefore, the equations (1) and (2) areapproximated by the following equations (3) and (4).

T ₁=1−A ₁   (3)

T ₂=1−R ₂   (4)

FIG. 5 is a schematic cross sectional view illustrating the reflection,transmission, and absorption of the light which entered the pixel. Alight intensity of incident light is assumed to be 1 and a reflectanceat the reflection plate is assumed to be R_(c). The light having a lightintensity of R₂ in the incident light is reflected by a surface 23 ofthe second light modulating layer and the light having a light intensityof T₂ passes through the second light modulating layer. With respect tothe transmission light having the light intensity of T₂, the lighthaving a light intensity which is R₁ times as large as the lightintensity of T₂ is reflected by a surface 24 of the first lightmodulating layer and the light having a light intensity which is T₁times as large as the light intensity of T₂ passes through the firstlight modulating layer. With respect to the light of T₁·T₂ which haspassed through the first light modulating layer, the light having alight intensity which is R_(c) times as large as the light intensity ofT₁·T₂, that is, the light having the light intensity which isT₁·T₂·R_(c) times as large as the light intensity of the light whichentered from the most-obverse surface is reflected by the reflectionplate and enters the first light modulating layer again. The lighthaving a light intensity which is T₁ times as large as the lightintensity of the incident light, that is, the light having the lightintensity which is T₁ ²·T₂·R_(c) times as large as the light intensityof the light which entered from the most-obverse surface passes throughthe surface 24 of the first light modulating layer. The transmissionlight passes through the surface 23 of the second light modulating layeragain and the light having a light intensity which is T₂ times as largeas the light intensity of the incident light passes through there.Therefore, the light intensity of the transmission light is T₁ ²·T₂²·R_(c) times as large as the light intensity of the light which enteredfrom the most-obverse surface. If the light having the light intensityof R₂ reflected by the surface 23 of the second light modulating layeris also added, the multiple reflection is ignored and the lightintensity of the reflection light is (R₂+T₁ ²·T₂ ²·R_(c)) times as largeas the light intensity of the incident light. Therefore, a reflectionlight intensity I is obtained by the following equation (5).

I=R ₂ +T ₁ ² ·T ₂ ² ·R _(c) =R ₂+(1−A ₁)²·(1−R ₂)² ·R _(c)   (5)

The reason why the color display, the black display, and the whitedisplay in which the reflectance is high can be performed by the abovedisplay apparatus will be sequentially described hereinbelow.

First, in the case of displaying a specific color, for example, red,both of the first light modulating layer 11 and the second lightmodulating layer 12 on the reflection plate 17 for reflecting thewavelength range of red are set into the transmitting state. That is,they are set into the state of T₁=T₂=1 and the first light modulatinglayers 13 and 15 on the reflection plates 18 and 19 for reflecting thewavelength ranges of blue and green are set into the absorbing state.Although the second light modulating layers 14 and 16 may be set intoeither the reflecting state or the transmitting state, they are set intothe transmitting state here. It is assumed that R_(c)=0.33 and thestates of the light modulating layers are summarized to the followingTABLE 1. TABLE 1 is a table in which with respect to each of the pixelshaving the reflection plates 17, 18, and 19 of red, green, and blue, theabsorptance of the first light modulating layer, the reflectance of thesecond light modulating layer, and the reflection light intensity Iwhich is calculated by the equation (5) are summarized. Although theexpressions such as “reflectance is equal to 1”, “absorptance is equalto 1”, “reflectance is equal to 0”, “absorptance is equal to 0”, and thelike are conceptually used here, it corresponds to the ideal state andthe perfect reflection and the perfect absorption are not necessarilyindispensable. This is true of the following expressions.

TABLE 1 States of light modulating layers at the time of the red displayReflectance 0 0 0 R₂ Absorptance 0 1 1 A₁ Reflection 0.33 0 0 lightintensity I Color of Red Green Blue reflection (reflection (reflection(reflection plate plate 17) plate 18) plate 19)

The incident light passes through the light modulating layers 11 and 12over the reflection plate 17 for reflecting the wavelength range of redand the red light is reflected by the reflection plate 17. Since thelight modulating layers 13 and 15 absorb the incident light and do notreflect and transmit the incident light, the pixels of blue and greenbecome black. Thus, only the red light is reflected and the red displayis performed.

Similarly, the states of the light modulating layers in the case ofdisplaying white are summarized to the following TABLE 2. At the time ofthe white display, since the whole incident light is reflected by thelight modulating layers, the white display is performed. That is,according to the embodiment, at the time of the white display, theincident light is not absorbed by the color filters or the like but thewhole incident light is reflected. Therefore, the white display of thehigh reflectance can be realized. Similarly, a construction in the caseof expressing black is summarized to the following TABLE 3.

TABLE 2 States of light modulating layers at the time of the whitedisplay Reflectance 1 1 1 R₂ Absorptance 0 0 0 A₁ Reflection 1 1 1 lightintensity I Color of Red Green Blue reflection (reflection (reflection(reflection plate plate 17) plate 18) plate 19)

TABLE 3 States of light modulating layers at the time of the blackdisplay Reflectance 0 0 0 R₂ Absorptance 1 1 1 A₁ Reflection 0 0 0 lightintensity I Color of Red Green Blue reflection (reflection (reflection(reflection plate plate 17) plate 18) plate 19)

Similarly, the gradation display from white to black can be alsorealized. The operation to express white of a reflectance n (0<n<1),that is, gray can be performed by adjusting the foregoing factors asillustrated in the following TABLE 4.

TABLE 4 States of light modulating layers at the time of the whitedisplay of the reflectance n to the black display Reflectance n n n R₂Absorptance 1 1 1 A₁ Reflection n n n light intensity I Color of RedGreen Blue reflection (reflection (reflection (reflection plate plate17) plate 18) plate 19)

By the combination as mentioned above, the color display can beperformed and the display of the high reflectance at the time of thewhite display can be realized. The above combination is an example andthe invention is not always limited to such a combination but a furthervariety of combinations can be made.

The reflection type display apparatus of each embodiment described abovecan be realized as either a display apparatus of a passive matrixdriving type or a display apparatus of an active matrix driving type. Aspacer is provided between the substrates 1 and 6 in order to keep aninterval between the substrates constant. The spacer is formed in anarbitrary shape such as cylindrical shape, spherical shape, orquadrangular prism shape.

Although the reflection type display apparatus of the passive matrixdriving type and the reflection type display apparatus of the activematrix driving type will be described hereinbelow with respect to theconstruction of the second embodiment illustrated in FIG. 3 as anexample, a similar construction can be also used in the first and thirdembodiments. The first embodiment uses the construction in which thethird electrode 5 is eliminated.

In FIG. 9, the colored second electrodes 4 are arranged on the substrate6 along a plurality of lines in one direction (assumed to be an Xdirection). The third electrodes 5 are arranged on the substrate 6 alonga plurality of lines in parallel with the second electrodes 4. Since thethird electrode 5 does not contribute to the display, it is formed by athin line having a width smaller than that of the second electrode 4.However, when the electroplating film is formed on the second electrode4, by forming the same electroplating film, the third electrode 5 can bemade to contribute to the display.

The first electrodes 2 having the light transmitting property arearranged on the substrate 1 having the light transmitting property alonga plurality of lines in the direction (assumed to be the Y direction)perpendicular to the X direction so as to intersect the secondelectrodes 4 arranged along a plurality of lines.

The shapes of the second electrode 4 and the third electrode 5 are notlimited to the shapes as illustrated in FIG. 9. As illustrated in a planview of FIG. 10B, the line-shaped electrode 5 having “-”-shaped(line-shaped) projecting portions on one side (one side in the Ydirection) so as to surround the electrode 4 in a

-character shape can be provided. As illustrated in a plan view of FIG.10C, the line-shaped electrode 5 having “-”-shaped (line-shaped)projecting portions on both sides (both sides in the Y direction) so asto surround the electrode 4 from the both sides can be also provided.FIG. 10A is a plan view of the electrodes 4 and 5 illustrated in FIG. 9.Although the scan of the electrodes 5 can be performed by selectivelysupplying a current every line, such an operation that two lines aresimultaneously selected, the current is supplied thereto, and the scanis shifted line by line can be also executed. According to such anoperation, for example, when the current is supplied from the electrode4 to the electrode 5, the current can be supplied from the electrode 4to the electrodes 5 of two lines.

The construction in which the electrode 5 is provided along one side ofthe electrode 4 as illustrated in FIG. 1A, the construction in which theelectrode 4 is surrounded by the electrode 5 in the “

”-character shape as illustrated in FIG. 10B, the construction in whichthe periphery of the electrode 4 is surrounded by the electrode 5 asillustrated in FIG. 10C can be also applied to the display apparatus ofthe active matrix driving type. However, in the case of the activematrix driving type, the electrode 4 and the electrode 5 are providedpixel by pixel.

In the case of the reflection type display apparatus of the activematrix driving type, as illustrated in FIG. 11, the electrode 4 and theelectrode 5 are arranged pixel by pixel, the electrode 4 is connected toa first switch T1 of a thin film transistor (TFT) or the like, and theelectrode 5 is connected to a third switch T3 of the thin filmtransistor (TFT) or the like. The electrodes 2 are constructed as acommon electrode. A second switch T2 of the thin film transistor or thelike controls an electric continuity of the first switch T1. A fourthswitch T4 of the thin film transistor or the like controls an electriccontinuity of the third switch T3. The second switch T2 and the fourthswitch T4 are connected to control terminals (functioning as gates inthe case where the switches are field effect transistors (FETs)) of thefirst switch T1 and the third switch T3, respectively. Control terminals(functioning as gates in the case where the switches are field effecttransistors) of the second switch T2 and the fourth switch T4 areconnected to scanning lines (functioning as gate lines in the case wherethe switches are field effect transistors) 28, respectively. By theon/off control of the second switch T2 and the fourth switch T4, a datasignal from a data line 29 is supplied to the control terminal of thefirst switch T1, a capacitor C1, the third switch T3, and a capacitorC2, respectively. The data signal is accumulated into the capacitors C1and C2. The first to fourth switches are provided pixel by pixel. By theon/off control of the first and third switches T1 and T3, the currenthaving the set current density flows through the first and thirdswitches. A ground (GND) line 31 is provided.

In the reflection type display apparatus of the passive matrix drivingtype and the reflection type display apparatus of the active matrixdriving type mentioned above, two kinds of voltages are switched andapplied to the electrodes 2, 4, and 5 by using a control signal circuit(serving as a control unit) illustrated in FIGS. 12, 13A, and 13B. Thecontrol signal circuit controls the current flowing direction among thethree electrodes 2, 4, and 5 illustrated in FIGS. 12, 13A, and 13B. Thatis, when the electrode 2 is assumed to be a cathode, the electrodes 4and 5 are assumed to be an anode, and the current is supplied to them,the electrode 2 is set to the GND and the electrodes 4 and 5 are set toa voltage V. When the electrode 4 is assumed to be the cathode, theelectrodes 2 and 5 are assumed to be the anodes, and the current issupplied to them, the electrode 4 is set to the GND and the electrodes 2and 5 are set to the voltage V. When the electrode 5 is assumed to bethe cathode, the electrodes 2 and 4 are assumed to be the anodes, andthe current is supplied to them, the electrode 5 is set to the GND andthe electrodes 2 and 4 are set to the voltage V.

In this manner, the control signal circuit provides the first mode inwhich the first electroplating film which forms the first surface thatis come into contact with the first electrode 2 is formed on the firstelectrode 2, the second mode in which the second electroplating filmwhich forms the second surface that is not come into contact with thesecond electrode 4 is formed on the second electrode 4, thereby settinga state where the first electroplating film does not exist on the firstelectrode 2, and the third mode in which the electroplating film isformed on the third electrode 5, thereby setting a state where the firstand second electroplating films do not exist on the first and secondelectrodes 2 and 4, respectively.

A size of pixel of the reflection type display apparatus of theembodiment is not particularly limited but is properly set according toan application. The pixel size can be set to, for example, a valuewithin a range from about 10 μm to tens of mm.

Although barriers adapted to partition the pixels are not provided inthe embodiment, such barriers may be provided as necessary. However, ifthe voltage which is applied across the pixels is equal to apredetermined critical voltage or less, no electroplating occurs and thepixel size can be set so that an influence of the adjacent pixel is notexerted. This point has also been disclosed in, for example, theOfficial Gazette of Japanese Patent Application Laid-Open No.2004-170850.

By using the reflection type display apparatus of the embodiment, thereflectance and the absorptance of the first surface of the film whichis formed by the electroplating and those of the second surface thereofdiffer. Specifically speaking, in the electroplating film, the surface(first surface) that is come into contact with the electrode hassmoothness similar to that of the electrode and becomes a mirrorsurface, so that the film color (first color) becomes the color of themetal itself to be electroplated. For example, if the metal is silver,the first color is white. The surface (second surface) that is not comeinto contact with the electrode, that is, the surface which is come intocontact with the liquid becomes a surface which is very rough and haslarge concave/convex shapes. While the incident light is repetitivelyreflected in the rough surface, it is absorbed, so that the film color(second color) becomes dark such as black, brown, or the like.

When comparing with the construction of the electrodes, in the casewhere the first electrode which is arranged on the obverse side iselectroplated, the color (first color) of the first surface is observed,and in the case where the second electrode which is arranged on the deepside through a plating liquid is electroplated, the color (second color)of the second surface is observed.

The larger the thickness of electroplating film is, the larger a colorconcentration is. That is, the larger the film thickness is, the higherthe reflectance of the first surface is and the higher the absorptanceof the second surface is. In both surfaces, the smaller the filmthickness is, the transmitting ratio rises and the film approaches atransparent state. The electroplating film thickness is almostproportional to a plating time and a current density and can becontrolled.

A third color which is realized by using the third electrode and isperformed by the state where the electroplating is not performed to thefirst and second electrodes can be expressed. The third color becomesthe color of the second electrode itself in the case where the secondelectrode is made of a substance adapted to reflect the light in aparticular wavelength range. The third color becomes transparent in thecase where the second electrode is made of a transparent substance. Whenthe third color is transparent, by laminating a reflection plate whichreflects the light in a particular wavelength range under the reflectiontype display apparatus, the specific color can be displayed.

As a more specific example, a reflection type display apparatus in whichthe first color is white, the second color is black, the secondelectrode is transparent, and the third color is determined by thereflection plate, or the like can be realized. In a state where thefirst electrode has been plated in white as a first color, the incidentlight is reflected without being subjected to the wavelength selection,so that the reflection at a high reflectance can be performed.Particularly, since the incident light is reflected over the wholewavelength range without being absorbed by the color filter or the likeas compared with the related art, the white display at a highreflectance can be obtained. Similarly, black as a second color and thethird color by the reflection plate can be displayed. By combining theforegoing states, the reflection type display apparatus which canperform the white display at the high reflectance and can perform thecolor display can be realized.

Subsequently, a specific apparatus construction of the invention will bedescribed with reference to FIGS. 4A to 4C. Glass having a thickness of0.7 mm is used as a substrate 1. An ITO film having a thickness of 150nm formed by a sputtering method is used as a first electrode 2. As anelectrolyte solution 3, a solution in which dimethylformamide (DMF) isused as a solvent, silver chloride of 300 mmol/L is used as anelectroplating seed, and copper-sulfate 5 hydrate of 100 mmol/L iscontained is used. This solution contains a solution in whichtetrabutyle ammonium bromide (TBAB) of 1 mol/L is used as a supportingelectrolyte and a glossy agent is contained. The pixel size is set to0.7 mm×0.7 mm and a thickness of the electrolyte layer 3 is set to 0.1mm. An ITO film similar to that of the first electrode 2 is used as asecond electrode 4. Silver is used as a third electrode 5. Glass is usedas a supporting substrate 6. The reflection plates 17, 18, and 19 eachfor reflecting the light of a particular wavelength range are providedfor the rear surface of the glass.

When the first electrode 2 is assumed to be the cathode, the secondelectrode 4 and the third electrode 5 are assumed to be the anodes, andan electric potential of 1.5V is applied to them, a current of 10 mA/cm²flows and the electroplating film is formed on the surface of the firstelectrode, so that white is observed from the obverse surface. When thesecond electrode 4 is assumed to be the cathode, the first electrode 2and the third electrode 5 are assumed to be the anodes, and the electricpotential of 1.5V is applied to them, the current of 10 mA/cm² flows andthe electroplating film is formed on the surface of the electrode 4, sothat black is observed from the obverse side.

When third electrode 5 is assumed to be the cathode, the first electrode2 and the second electrode 4 are assumed to be the anodes, and anelectric potential of 1.5V is applied to them, the current of 10 mA/cm²flows and the electroplating film formed on the surfaces of theelectrodes 2 and 4 are dissolved and extinguished. After the incidentlight passed through the electrodes 2 and 4, it is reflected by thereflection plates 17, 18, and 19 and passes through the electrodes 2 and4 again. Therefore, the color of the wavelength range reflected by thereflection plates is observed from the obverse surface. Although thereflection plate is used as a reflector in the embodiment, the reflectorcan be constructed by forming a reflecting layer which reflects thelight of the specific color onto the substrate 6 pixel by pixel byprinting or the like. The reflector may be constructed by forming acolor filter onto the substrate 6 and arranging the reflection plateonto the color filter.

In the embodiment, besides the glass, a solid having a lighttransmitting property such as a resin can be used as a substrate havingthe light transmitting property which protects the obverse surface. Forthe first electrode 2 and the second electrode 4, besides the ITO, IZO(Indium-Zinc-Oxide), zinc oxide, titanium oxide, or another conductivetransparent substance can be used as a material of the transparentelectrode. A metal thin film or a mesh structure or comb-tooth structureof a metal can be also used so long as it has the light transmittingproperty. For the third electrode 5, platinum, carbon, gold, or the likecan be used so long as it is a conductor of the same kind as that of themetal which is electroplated or a stable conductor which is not changedby the electroplating reaction. Besides them, a transparent materialsuch as ITO or the like can be also used. In the case where theelectrode 4 is colored and has characteristics adapted to reflect thelight in the particular wavelength range, the reflection plates 17, 18,and 19 of the pixel can be omitted. Each of the reflection plates 17,18, and 19 is formed by arranging colored paper onto a glass substratehaving a thickness of 0.1 mm. The reflection plate is laminated onto thesubstrate 6 so that the paper is come into contact with the substrate 6.

By constructing the reflection plates 17, 18, and 19 of the reflectiontype display apparatus of the embodiment as reflection plates of threecolors of red, green, and blue and arranging them by a Bayer layout in amatrix form, the reflection type display apparatus which can perform thecolor display is formed. The pixels are driven by an active matrixdriving manner using transistors. A color layout of the reflectionplates is not limited to the Bayer layout. A color arrangement is notlimited to the foregoing construction but a construction of cyan,magenta, and yellow may be used. The pixels may be driven by a passivematrix driving manner using crossed electrodes.

Fourth Embodiment

FIG. 6 is a cross sectional view of a pixel of a reflection type displayapparatus of the fourth embodiment of the invention. FIG. 6 has aconstruction in which a diffusion sheet 26 is further added to theconstruction in FIG. 3 or FIGS. 4A to 4C. By using the diffusion sheet26, a viewing angle is widened more than that of the reflection typedisplay apparatus of FIG. 3 or FIGS. 4A to 4C and a display image iscloser to an image of the paper and the image can be displayed so thatit can be easily seen.

A position where the diffusion sheet 26 is arranged is not limited tothe most-obverse surface but may be set to an arbitrary position on theobverse surface side rather than the “metal film which reflects thelight” which is formed by the electroplating. A material is not limitedto the diffusion sheet but another member may also have a diffusingfunction. For example, a structure in which the supporting substrate 1or the first electrode 2 has the light diffusing effect may be used.

Fifth Embodiment

FIG. 7 is a cross sectional view of a pixel of a reflection type displayapparatus of the fifth embodiment of the invention. In order to obtainan effect similar to that in the embodiment 2, a concave/convex patternhaving a pitch of 0.05 mm is formed by a photolithographing step and awet etching on the surface of the transparent electrode 2 in FIG. 3 orFIGS. 4A to 4C which is come into contact with the electrolyte solution3. Other constructions are similar to those in FIG. 3 or FIGS. 4A to 4C.If a metal film which reflects the light is electroplated onto thetransparent electrode 2 having the concave/convex pattern, since thelight is scattered by the concave/convex shapes, the white displayhaving good quality near the paper can be performed. It is sufficientthat the concave/convex pattern has a function for scattering the lightand it is needless to say that a pitch size, a layout, an electrodematerial, and the like are not limited to the foregoing numerical valuesand the like.

Sixth Embodiment

FIG. 8 is a cross sectional view of a pixel of a reflection type displayapparatus of the sixth embodiment of the invention. FIG. 8 has aconstruction similar to that in FIG. 3 or FIGS. 4A to 4C except that thesecond electrode 4 is made of a transparent material and a multilayerfilm 27 as a reflector constructed so as to reflect the light in theparticular wavelength range is arranged between the supporting substrate6 and the second electrode 4. By laminating a film having a thickness ofn·d=m·λ/2 (n denotes a refractive index, d a film thickness, and m aninteger) for a wavelength λ of the light to be reflected and having adifferent refractive index, the good selective reflection can beperformed.

For example, in order to reflect blue having a wavelength of 450 nm, byalternately laminating three layers of a film made of silica and havinga thickness of 308 nm (a refractive index is equal to 1.46) and a filmmade of titania and having a thickness of 180 nm (a refractive index isequal to 2.5), the blue light can be desirably reflected.

The green light having a wavelength of 550 nm can be reflected bylaminating three layers of a silica film of 377 nm and a titania film of220 nm. The red light having a wavelength of 700 nm can be reflected bylaminating three layers of a silica film of 479 nm and a titania film of280 nm. In order to allow a desired pixel to have desired reflectingcharacteristics, the photolithography and the etching can be used. Amaterial and a thickness of the multilayer film are not limited to thembut proper material and thickness can be selected according to anecessary wavelength range to be reflected.

Seventh Embodiment

It is an object of the embodiment to provide a display apparatus of anelectrodepositing type which can continuously maintain an image for along time. According to the embodiment, there is provided a displayapparatus in which an electroplating is formed on an electrode and whichis used for modulating light, wherein a layer having an insulator havingair gaps therein and conductive fine particles dispersed in the air gapsis formed on the electrode. According to the embodiment, a displaycontrast can be further raised, a deterioration in display contrast thatis caused by redissolution of a deposited metal can be suppressed, and adisplay holding period can be improved.

FIG. 16 illustrates a schematic cross sectional view of the firstelectrode 2 in which nothing is formed on the surface as a firstcomparative example. FIG. 16 illustrates a state where an electroplatingprocess has been executed and metal has been deposited as anelectroplating. In the case of such a construction in the related art,when a relatively high voltage is applied in order to raise a responsespeed, metal ions serving as an electroplating layer are deposited in aparticle shape onto the electrode 2. Therefore, a coloring efficiencyand the contrast deteriorate. There is such a problem that since acontact area between a deposited metal 203 and the solution is large, ifthe metal is left, the metal 203 is redissolved, the display isweakened, and the contrast deteriorates.

Subsequently, as a second comparative example, FIGS. 17A and 17Billustrate schematic diagrams in the case where a layer formed byconductive fine particles 202 is formed on the electrode as disclosed inthe Official Gazette of Japanese Patent Application Laid-Open No.2005-092183. FIG. 17A illustrates a state before the electroplating isexecuted. FIG. 17B illustrates a state where the metal has beendeposited as an electroplating layer after the electroplating processwas executed. In this case, an amount of deposited metal 203 increasesowing to a surface area effect by the conductive fine particles 202 andthe contrast rises. However, also in this case, since the contact areawhere the deposited metal 203 is come into contact with the solution islarge, if the metal is left, the deposited metal 203 is redissolved, thedisplay is weakened, and the contrast deteriorates. Such a phenomenonoccurs by the following reasons. First, since the conductive fineparticles are come into contact with the solution and exist densely, thecurrent becomes liable to flow in the conductive fine particles by theapplied voltage and the deposition of the metal particles occurs mainlyon the most-obverse surface of the electrode. Second, since there are nosubstances which obstruct the contact between the deposited metalparticles and the solution, the metal is easily redissolved.

For the construction as mentioned above, a layer 1003 in which theconductive fine particles 202 have been dispersed in air gaps of aninsulator 201 having the air gaps therein is formed on the firstelectrode 2 in the embodiment. FIGS. 14, 15A, and 15B illustrateenlarged diagrams of the layer 1003 in which the conductive fineparticles have been dispersed in the air gaps of the insulator havingthe air gaps therein is formed on the transparent electrode 2. FIG. 15Aillustrates a state before the electroplating is executed. FIG. 15Billustrates a state where the metal has been deposited after theelectroplating process was executed. As illustrated in FIG. 15A, sincethe conductive fine particles 202 have been dispersed in the air gaps inthe insulator, a state where the conductive fine particles 202 existdensely as disclosed in the related art does not occur. Since theconductive fine particles 202 exist in such air gaps, the contact areabetween the conductive fine particles and the solution is remarkablyreduced.

If a ratio (porosity) of the air gaps to the whole volume of the layerwhich is formed by the insulator 201 is too small, since an amount ofelectroplating which can be deposited in the air gaps decreases, thereis a possibility that a sufficient light shielding property cannot beobtained. Therefore, the insulator 201 has to be thickened in order toobtain the sufficient light transmitting property and it is undesirable.This is because if the insulator 201 is too thick, an amount of lightscattering increases and the sufficient light shielding property cannotbe obtained at the time of the transmitting display. Therefore, theporosity is set to, desirably, 5% or more, and much desirably, 50% ormore. With respect to a size of air gap (air gap size), it is demandedthat the air gap size is sufficiently smaller than the pixel size. Thisis because if the air gap size is larger than the pixel size, a currentdensity in the pixel does not become uniform. For example, a porouslayer whose partition is extremely thin or the like can be used sinceits porosity is large and the air gap size is small.

As illustrated in FIG. 15B, in the case where the first electrode 2 hasthe layer in which the conductive fine particles 202 have been dispersedin the air gaps of the insulator 201 having the air gaps therein, if theelectroplating is performed, the metal ions are deposited in a particleshape onto the conductive fine particles 202 so as to embed the airgaps. This is because of the following reasons. In an electrode in whichthe fine particles of the insulator 201 and the conductive fineparticles 202 have been mixed and sintered on the surface, theconductive fine particles 202 are come into contact with each other andare mutually conductive. There are also portions where the conductivefine particles 202 and the transparent electrode 2 are in contact witheach other. Therefore, the electric coupling in a range from thetransparent electrode 2 to a plurality of conductive fine particles 202exists at a plurality of positions in the pixel. The current flows fromthe transparent electrode 2 to the electroplating liquid through theplurality of conductive fine particles 202. Therefore, theelectroplating occurs near a front edge of the conductive fine particle202. Further, by such a chain reaction that the fine particles of themetal 203 which grew by the electroplating are coupled with neighboringother conductive fine particles 202 or the like, the portion where theelectroplating occurs changes moment by moment and the deposition of thefine particles of the metal 203 occurs at a plurality of positions inthe porous layer.

The insulator 201 plays a role of what is called a footing forsupporting the conductive fine particles 202. Therefore, if theinsulator 201 has conductivity, since the fine particles depositing stepis not satisfied, it is demanded that the insulator 201 is insulative.If the electric potential is shut off, the metal 203 which wasfield-deposited in the above step is naturally redissolved according toa diffusion rule. However, if a concentration of the metal in theambient solution is high, the dissolution is suppressed. Since thecirculation of the solution is suppressed in the porous layer, theredissolved metal ions are difficult to be diffused into the wholesolution, so that the metal concentration in the solution is held high.Consequently, the redissolution can be suppressed by using the porouslayer. Although the “suppression of the field deposition” due to theporous layer also occurs at the time of the field deposition by the samemechanism, it can be solved by raising a deposition potential.

The contact between the electrolyte solution and the metal serving as adeposited electroplating can be suppressed by the reasons as mentionedabove, so that the dissolution of the metal 203 into the solution can bereduced.

The following material can be desirably used as an insulator 201 havingthe air gaps therein: for example, an inorganic insulative material suchas titanium oxide, silicon oxide, zinc oxide, or aluminum oxide; theirmixture; glass; or the like. An organic insulative material such aspolymethyl methacrylate (PMMA), polystyrene, silicone, cellulose,polycarbonate, polyethylene, polypropylene, or polyethyleneterephthalate, or the like can be also used. To raise the contrast, itis desirable that the layer in which the conductive fine particles 202have been dispersed in the insulator 201 having the air gaps therein istransparent. It is, therefore, much desirable that the insulator 201 hasthe light transmitting property for the visible light and its refractiveindex is close to that of the electrolyte solution. Since a refractiveindex of water, propylene carbonate, gamma-butyrolactone,dimethylformamide, or the like which is used for the electrolytesolution is generally so small to be equal to 1.5 or less, it isdesirable that the refractive index of the insulator 201 having the airgaps therein is equal to about 2 or less. As an inorganic insulativematerial having such a feature, silicon oxide, aluminum oxide, or thelike can be mentioned. It is, therefore, much desirable to use a mixturecontaining them as a main component, glass, or the like. An organicinsulative material such as polymethyl methacrylate (PMMA), polystyrene,silicone, or the like is also suitable because its refractive index issmall.

As a structure of the layer of the insulator 201 having the air gapstherein, there can be used: a structure in which insulative fineparticles are stacked; a structure in which the conductive fineparticles 202 are dispersed into porous glass by a sol-gel method, or astructure in which the conductive fine particles 202 are dispersed intoa porous resin. Particularly, the stacked layer of the insulative fineparticles is suitable because it can be easily produced by dispersingand mixing the insulative fine particles and the conductive fineparticles 202 into a solvent, coating the electrode with the resultantmixture, and sintering them.

In the structure in which the insulative fine particles are stacked asmentioned above, an inorganic insulative material such as titaniumoxide, silicon oxide, zinc oxide, alumina, or the like, their mixture,glass, or the like can be used as insulative fine particles. An organicinsulative material such as polymethyl methacrylate (PMMA), polystyrene,silicone, cellulose, polycarbonate, or the like can be also used. Amongthem, particularly, silicon oxide, aluminum oxide, or the like, amixture containing them as a main component, glass, polymethylmethacrylate (PMMA), polystyrene, or silicone is suitable in terms of apoint that it is not dissolved into the organic solvent and a point thatthe refractive index is small.

Metal fine particles of platinum or the like or particles of generalmetal oxide can be used as conductive fine particles 202. From aviewpoint of the contrast, it is desirable that the layer 1003 in whichthe conductive fine particles 202 have been dispersed in the air gaps ofthe insulator 201 having the air gaps therein is transparent. It is,therefore, desirable that the conductive fine particles 202 are made ofa metal oxide. Specifically speaking, zinc oxide, indium oxide, tinoxide, or the like, or a material obtained by doping impurities to themis desirable. Specifically speaking, ITO, F-doped tin oxide, a mixtureof them, or the like can be mentioned. Particularly, indium oxide or tinoxide which is difficult to be oxidized/reduced by the electroplating isdesirable.

Since the conductive fine particles 202 are dispersed in the air gaps inthe insulator 201, the metal 203 is deposited into the air gaps uponelectroplating. It is, therefore, desirable that a mean diameter of theconductive fine particles 202 is sufficiently smaller than the air gapsin the insulator 201. Therefore, in the method of stacking theinsulative fine particles, it is desirable that the mean diameter of theconductive fine particles is smaller than a mean diameter of theinsulative fine particles. Since the conductive fine particles have therelatively large refractive index and are liable to scatter the light,it is desirable that the mean diameter of the conductive fine particlesis less than 100 nm.

The elements disclosed in the foregoing embodiment are suitably used asan element of the metal 203 which is deposited by the electroplatingprocess.

Although Examples of the embodiment will be described hereinbelow, theinvention is not limited to the following Examples.

EXAMPLE 1

In this Example, the apparatus structure illustrated in FIG. 14 ismanufactured. Glass having a thickness of 0.7 mm is used as a substrate1. An ITO film having a thickness of 150 nm formed by the sputteringmethod is used as a first electrode 2. As an electrolyte solution 3, asolution in which propylene carbonate (PC) is used as a solvent, silversulfate of 0.033 mol/L is used as an electroplating seed, tetraethylammonium bromide (TEAB) of 0.267 mol/L is used as an electrolyte, and aglossy agent is contained is used. A pixel size is set to 0.7 mm×0.7 mm.A thickness of electrolyte solution 104 is set to 0.1 mm. Silver is usedfor a counter electrode 105. Glass is used for a supporting substrate106. The layer 1003 in which the conductive fine particles have beendispersed in the insulator having the air gaps therein is formed by fineparticles of silicon oxide and fine particles of tin oxide. In thisinstance, colloidal silica PL-20 (grain diameter is equal to 220 nm)produced by Fuso Chemical Industry Co., Ltd. is used as silicon oxideand tin oxide sol EPS-6 (grain diameter is equal to 5 nm) produced byYamanaka Industry Co., Ltd. is used as tin oxide. A producing method ofthe layer 1003 will be described hereinbelow.

First, colloidal silica PL-20 of 2 ml and tin oxide sol EPS-6 of 2 mlare mixed and the solution is mixed by a stirrer for about 10 minutes.After that, polyethylene glycol (molecular weight is equal to 20000) of3 g is added, a viscosity is adjusted, and its paste is sufficientlykneaded for about 10 minutes. Subsequently, a polyimide tape (trademark:Kapton) is adhered onto the ITO substrate so as to mask its both endsand is fixed. Then, the paste is dropped and spread by slide glass,thereby coating with the paste having a thickness of about 50 μm of thepolyimide tape. The paste is dried for 20 minutes at temperatures of 160to 200° C. Subsequently, a temperature is raised from a room temperatureto 450° C. for 30 minutes, a sintering is performed at 450° C. for 30minutes, and an annealing is naturally performed to the roomtemperature.

As for the film formed as mentioned above, in the air, since the lightis scattered, the film shows a cloudy external appearance. However, inthe solution, since the liquid permeates, the film shows an almosttransparent external appearance.

On the other hand, an apparatus having a texture SnO₂ electrode (TCOsubstrate for a solar battery: Al0U80 produced by Asahi Glass Co., Ltd.)in which silver is deposited in a particle shape in the related art isprepared as Comparative Example 1. An apparatus having another electrodein the related art is also prepared as Comparative Example 2. Aproducing method of such electrodes will now be described. First,conductive fine particles (FS-10P produced by Ishihara Sangyo Kaisha,Ltd.) of 3.7 g are mixed into the pure water of 16 ml, thereafter,polyethylene glycol (molecular weight is equal to 20000) of 0.37 g isadded, and a viscosity is adjusted. Its paste is sufficiently kneadedfor about 10 minutes. After that, the ITO substrate is coated with thepaste and the paste is dried and sintered in a manner similar to Example2.

Subsequently, the electroplating is executed by using the firstelectrode 2 in this Example in which the layer 1003 in which theconductive fine particles were dispersed in the insulator having the airgaps therein has been formed on the surface and the second electrode 4made of silver. According to the electrodes of Comparative Examples 1and 2, the electroplating process is also similarly executed.Specifically speaking, a voltage of 3.5V is applied to theelectroplating liquid for 20 seconds so that the first electrode 2 isset to a negative polarity, thereby depositing the electroplating layer.

A section SEM observation is performed to the electroplating of Exampleformed in this manner. Thus, it has been found that in the air gaps inthe insulator in the layer 1003 in which the conductive fine particleswere dispersed in the insulator having the air gaps therein, the silverparticles of 100 to 200 nm were deposited while setting the conductivefine particle to a start point. An external appearance in which areflectance is small and it is desirably black is obtained.

Subsequently, the electroplating films of Comparative Examples 1 and 2are also similarly observed. Thus, it has been found that the colors ofthe electroplating films are black and their transmitting ratios andreflectances are small. It has also been found that the electroplatingof Comparative Example 1 has such a structure that the silver particlesof 100 to 200 nm are distributed on the surface of the electrode in aparticle form. It has also been found that the electroplating ofComparative Example 2 has such a structure that silver is hardlydeposited in the air gaps formed by the conductive fine particles andthe silver particles of 100 to 200 nm are distributed near the surfacein a particle form.

Subsequently, those electroplating films are held in the electroplatingsolution and changes in transmitting ratios and reflectances of theelectroplating films are examined. FIGS. 18A and 18B are diagrams ineach of which the changes in transmitting ratios and reflectances to adipping time into the electroplating solution are plotted. It will beunderstood from FIGS. 18A and 18B that in Example 1 (solid line), theinitial transmitting ratio is equal to 4%, the reflectance is equal toabout 10 to 12%, and the good black can be displayed. On the other hand,in each of Comparative Examples 1 (dot and bar line) and 2 (dottedline), it will be understood that the transmitting ratio rises with theelapse of the time and silver is dissolved in the solution. According tothe electroplating film of Example 1, however, it will be understoodthat since the time-dependent increase in transmitting ratio is smallerthan and an increase in reflectance is similar to that of each of theComparative Examples 1 and 2, better display memory performance isobtained.

EXAMPLE 2

In this Example, the layer 1003 in which the conductive fine particleshave been dispersed in the insulator having the air gaps therein isproduced by fine particles of aluminum oxide and fine particles of tinoxide.

As a film 1003, easy-sintering alumina TM-5 (grain diameter is equal to200 nm) produced by Daimei Chemical Industry Co., Ltd. is used asaluminum oxide, tin oxide sol EPS-6 (grain diameter is equal to 5 nm)produced by Yamanaka Industry Co., Ltd. is used as tin oxide, and themixing, coating, drying, and baking are executed in a manner similar toExample 1. Those films are held in the electroplating solution andchanges in transmitting ratios and reflectances of the electroplatingfilms are observed. Thus, it has been found that in a manner similar toExample 1, an increase in transmitting ratio is smaller than that ofeach of compared with Comparative Examples 1 and 2 and better displaymemory performance is obtained.

EXAMPLE 3

In this Example, the layer 1003 in which the conductive fine particleshave been dispersed in the insulator having the air gaps therein isproduced by fine particles of polymethyl methacrylate and fine particlesof tin oxide.

First, EPOSTAR (registered trademark) MX MX100W (grain diameter is equalto 150 to 200 nm) produced by Nippon Shokubai Co., Ltd. is prepared aspolymethyl methacrylate and tin oxide sol EPS-6 (grain diameter is equalto 5 nm) produced by Yamanaka Industry Co., Ltd. is prepared as tinoxide. The mixing, coating, drying, and baking at a temperature of 150°C. are executed by using them in a manner similar to Example 1. Thosefilms are held in the electroplating solution and changes intransmitting ratios and reflectances of the electroplating films areobserved. Thus, it has been found that in a manner similar to Example 1,an increase in transmitting ratio is smaller than that of each of theComparative Examples 1 and 2 and better display memory performance isobtained.

EXAMPLE 4

In this Example, the layer 1003 in which the conductive fine particleshave been dispersed in the insulator having the air gaps therein isproduced by fine particles of polystyrene and fine particles of tinoxide.

Microsphere 3200A (grain diameter is equal to 200 nm) produced byMoritex Corporation is used as polystyrene and tin oxide sol EPS-6(grain diameter is equal to 5 nm) produced by Yamanaka Industry Co.,Ltd. is used as tin oxide. The mixing, coating, drying, and baking at atemperature of 150° C. are executed in a manner similar to Example 1.Those films are held in the electroplating solution and changes intransmitting ratios and reflectances of the electroplating films areobserved. Thus, it has been found that in a manner similar to Example 1,an increase in transmitting ratio is smaller than that of each of theComparative Examples 1 and 2 and better display memory performance isobtained.

EXAMPLE 5

In this Example, the layer 1003 in which the conductive fine particleshave been dispersed in the insulator having the air gaps therein isproduced by fine particles of silicone and fine particles of tin oxide.

Silicon resin powder X-52-854 (grain diameter is equal to 800 nm)produced by Shin-Etsu Chemical Co., Ltd. is used as silicone and tinoxide sol EPS-6 (grain diameter is equal to 5 nm) produced by YamanakaIndustry Co., Ltd. is used as tin oxide. The mixing, coating, drying,and baking at a temperature of 300° C. are executed in a manner similarto Example 1. Those films are held in the electroplating solution andchanges in transmitting ratios and reflectances of the electroplatingfilms are observed. Thus, it has been found that in a manner similar toExample 1, an increase in transmitting ratio is smaller than that ofeach of the Comparative Examples 1 and 2 and better display memoryperformance is obtained.

EXAMPLE 6

In this Example, the layer 1003 in which the conductive fine particleshave been dispersed in the insulator having the air gaps therein isproduced by fine particles of silicon oxide and fine particles of ITOcontaining indium oxide as a main component.

Colloidal silica PL-20 (grain diameter is equal to 220 nm) produced byFuso Chemical Industry Co., Ltd. is used as silicon oxide and NANOTEKITO (grain diameter is equal to 30 nm) produced by CI Chemical IndustryCo., Ltd. is used as ITO. The mixing, coating, drying, and baking at atemperature of 450° C. are executed in a manner similar to Example 1.Those films are held in the electroplating solution and changes intransmitting ratios and reflectances of the electroplating films areobserved. Thus, it has been found that in a manner similar to Example 1,an increase in transmitting ratio is smaller than that of each of theComparative Examples 1 and 2 and better display memory performance isobtained.

EXAMPLE 7

In this Example, the layer 1003 in which the conductive fine particleshave been dispersed in the insulator having the air gaps therein isproduced by fine particles of silicon oxide and fine particles of zincoxide.

Colloidal silica PL-20 (grain diameter is equal to 220 nm) produced byFuso Chemical Industry Co., Ltd. is used as silicon oxide and NANOTEKITO (grain diameter is equal to 34 nm) produced by CI Chemical IndustryCo., Ltd. is used as zinc oxide. The mixing, coating, drying, and bakingat a temperature of 450° C. are executed in a manner similar toExample 1. Those films are held in the electroplating solution andchanges in transmitting ratios and reflectances of the electroplatingfilms are observed. Thus, it has been found that in a manner similar toExample 1, an increase in transmitting ratio is smaller than that ofeach of the Comparative Examples 1 and 2 and better display memoryperformance is obtained.

The invention can be used for the reflection type display apparatus inwhich the reflectance at the time of the white display is high and thegood black display can be performed or the reflection type displayapparatus in which the color display is demanded in addition to thewhite display and the black display. For example, the invention can beused for an advertisement apparatus, an image display apparatus fordisplaying photographs of a digital camera or the like, a message board,electronic paper, or the like. The invention can be also used for areflection type display apparatus of a segment type such as a watch orthe like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Applications No.2008-210527, filed Aug. 19, 2008, and No. 2008-191049, filed Jul. 24,2008 which are hereby incorporated by reference herein in theirentirety.

1. A reflection type display apparatus using an electroplating formodulating light comprising: a first electrode; a second electrode; andan electrolyte solution arranged between the first and secondelectrodes, wherein the electroplating is formed from the electrolytesolution onto one of the first and second electrodes by setting adirection of current flowing between the first and second electrodes, afirst surface of the electroplating formed on the first electrode suchthat the electroplating contacts the first electrode through the firstsurface is different in at least one of a light reflectance and a lightabsorptance from a second surface of the electroplating formed on thesecond electrode such that the electroplating does not contact thesecond electrode through the second surface, and a displaying isperformed by a reflection light from the first surface in case that theelectroplating is formed on the first electrode, while a displaying isperformed by a reflection light from the second surface in case that theelectroplating is formed on the second electrode.
 2. The reflection typedisplay apparatus according to claim 1, wherein the electrolyte solutioncontains, as an electroplating seed, a first metal element, and a secondmetal element of which oxidation-reduction potential is close to (seeline 2 in paragraph (0037)) that of the first metal element.
 3. Thereflection type display apparatus according to claim 2, wherein thefirst metal element is silver, and the second metal element is copper.4. The reflection type display apparatus according to claim 1, whereinthe first and second electrodes are disposed in opposition to eachother, and the reflection type display apparatus further comprises athird electrode disposed in opposition to at least one of the first andsecond electrodes, and in adjacent to the other of the first and secondelectrodes.
 5. The reflection type display apparatus according to claim1, wherein the second electrode has a property of light transmitting, areflector reflecting a radiation in a particular wavelength range isdisposed at a side is disposed at a side of the second electrodeopposite to the first electrode.
 6. The reflection type displayapparatus according to claim 4, further comprises a control unit forcontrolling the direction of current flowing between the first, secondand third electrodes, and the control unit has a first mode for forming,on the first electrode, a first electroplating forming the first surfacecontacting the first electrode, a second mode for forming, on the secondelectrode, a second electroplating forming the second surface notcontacting the second electrode, and setting that no firstelectroplating is disposed on the first electrode, and a third mode forforming an electroplating on the third electrode, and setting that nofirst electroplating is disposed on the first electrode and no secondelectroplating is disposed on the second electrode.
 7. The reflectiontype display apparatus according to claim 1, wherein the secondelectrode is formed from a material reflecting a radiation in aparticular wavelength range.
 8. The reflection type display apparatusaccording to claim 1, further comprising a first substrate has aproperty of light transmitting, and a second substrate disposed inopposition to the first substrate, wherein the first electrode isdisposed on the first substrate, and the second electrode is disposed onthe second substrate.
 9. The reflection type display apparatus accordingto claim 1, wherein a plurality of the second electrodes are arrangedalong a plurality of lines in one direction, and a plurality of thefirst electrodes are arranged along a plurality of lines in a directionperpendicular to the one direction, so as to cross the second electrode.10. The reflection type display apparatus according to claim 1, whereinone of the first and second electrodes is arranged in a matrix, and isconnected electrically to a first switch, a current flows through thefirst switch between the first and second electrodes, a second switch isconnected to a control terminal of the first switch for controlling anelectric continuity of the first switch, and the one of the first andsecond electrodes, and the first and second electrodes are providedpixel by pixel.